Extra doped region for back-side deep trench isolation

ABSTRACT

The present disclosure, in some embodiments, relates to a method of forming an image sensor. The method includes implanting a dopant into a substrate to form a doped region and implanting one or more additional dopants into the substrate to form an image sensing element between the doped region and a front-side of the substrate. The doped region directly contacts a boundary of the image sensing element that is furthest from the front-side of the substrate. The method further includes etching the substrate to form one or more trenches extending into a back-side of the substrate. The back-side of the substrate opposes the front-side of the substrate. The method further includes filling the one or more trenches with one or more dielectric materials to form isolation structures.

REFERENCE TO RELATED APPLICATION

This Application is a Divisional of U.S. application Ser. No.15/919,784, filed on Mar. 13, 2018, which is a Continuation of U.S.application Ser. No. 14/923,635 filed on Oct. 27, 2015 (now U.S. Pat.No. 9,954,022, issued on Apr. 24, 2018). The contents of theabove-referenced matters are hereby incorporated by reference in theirentirety.

BACKGROUND

Digital cameras and optical imaging devices employ image sensors. Imagesensors convert optical images to digital data that may be representedas digital images. An image sensor typically includes an array of pixelsensors, which are unit devices for the conversion of an optical imageinto electrical signals. Pixel sensors often manifest as charge-coupleddevices (CCDs) or complementary metal oxide semiconductor (CMOS)devices. However, CMOS pixel sensors have recently received moreattention. Relative to CCD pixel sensors, CMOS pixel sensors providelower power consumption, smaller size, and faster data processing.Further, CMOS pixel sensors provide a direct digital output of data, andgenerally have a lower manufacturing cost compared with CCD pixelsensors.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of a CMOS(complementary metal-oxide-semiconductor) image sensor having a lightsensing element separated from a deep trench isolation (DTI) structureby a doped region.

FIG. 2 illustrates a cross-sectional view of some embodiments of anintegrated chip comprising a photodiode separated from a back-side deeptrench isolation (BDTI) structure by a doped region.

FIG. 3 illustrates a cross-sectional view of some additional embodimentsof a BSI-CMOS image sensor comprising a photodiode separated from a BDTIstructure by a p-type doped region.

FIGS. 4-11 illustrate some embodiments of cross-sectional views showinga method of forming a CMOS-BSI image sensor having a doped regionseparating a photodiode and a BDTI structure.

FIG. 12 illustrates a flow diagram of some embodiments of a method offorming a CMOS-BSI image sensor having a doped region separating animage sensing element from a BDTI structure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Many portable electronic devices (e.g., cameras, cellular telephones,computers, etc.) include an image sensor for capturing images. Oneexample of such an image sensor is a CMOS image sensor (CIS) includingan array of active pixel sensors (APSs). Deep trench isolation (DTI)structures are often arranged between adjacent pixels of a CIS toisolate neighboring pixels. These DTI structures are formed by using anetch process to form a deep trench within the semiconductor substrate,which is then filled with an insulating material. In some applications,a functional layer is disposed over an upper surface of thesemiconductor substrate prior to etching the deep trench. The functionallayer can enhance the performance of the semiconductor device, but alsocomprises one or more potential contaminants for the substrate.

In some instances, the etch process used to form the deep trenchdissociates these contaminants from the functional layer, and thedissociated contaminants then diffuse into the semiconductor substratethrough sidewalls of the deep trench as the deep trench is being formed.These contaminants can degrade performance CIS by introducing interfacedefects near an edge of the DTI structure. The interface defects canlead to an increase in dark current and/or white pixel number. Theincrease in dark current causes charges to accumulate even when light isnot impingent on the image sensors, thereby becoming a major source ofnoise that can degrade image quality of digital imaging devices.

The present disclosure relates to a CMOS image sensor comprising a dopedregion, arranged between deep trench isolation structures and an imagesensing element, which is configured to reduce dark current and whitepixel number, and an associated method of formation. In someembodiments, the CMOS image sensor has a pixel region disposed within asemiconductor substrate. The pixel region has an image sensing elementconfigured to convert radiation into an electric signal. A plurality ofback-side deep trench isolation (BDTI) structures extend into thesemiconductor substrate on opposing sides of the pixel region. A dopedregion is laterally arranged between the BDTI structures and separatesthe image sensing element from the BDTI structures and the back-side ofthe semiconductor substrate. Separating the image sensing element fromthe BDTI structures prevents the image sensing element from interactingwith interface defects near edges of the BDTI structures, and therebyeffectively reduces dark current and improves white pixel numberperformance without any adverse side-effect.

FIG. 1 illustrates a cross-sectional view of some embodiments of a CMOS(complementary metal-oxide-semiconductor) image sensor 100 having alight sensing element separated from a deep trench isolation (DTI)structure by a doped region.

The CMOS image sensor 100 comprises a semiconductor substrate 102 havinga plurality of pixel regions 103 a-103 c. The plurality of pixel regions103 a-103 c respectively comprise an image sensing element 104configured to convert incident radiation 120 (e.g., photons) into anelectric signal. In some embodiments, the image sensing element 104 maycomprise a photodiode. In such embodiments, the photodiode may comprisea first region within the semiconductor substrate 102 having a firstdoping type (e.g., n-type doping) and an adjoining second region withinthe semiconductor substrate 102 having a second doping type (e.g.,p-type doping) that is different than the first doping type. In someembodiments, the plurality of pixel regions 103 a-103 c may be arrangedwithin the semiconductor substrate 102 in an array comprising rowsand/or columns.

The pixel regions 103 a-103 c are isolated from adjacent pixel regions103 a-103 c by deep trench isolation (DTI) structures 111 extending intothe semiconductor substrate 102 and comprising one or more dielectricmaterials 112-114. In some embodiments, the one or more dielectricmaterials 112-114 may comprise a passivation layer 112 and a dielectricfill layer 114 (e.g., an oxide), for example. In some embodiments, theDTI structures 111 may comprise back-side deep trench isolation (BDTI)structures that vertically extend from a back-side of the semiconductorsubstrate 102 to a location within the semiconductor substrate 102. Theback-side of the semiconductor substrate 102 opposes aback-end-of-the-line (BEOL) metallization stack comprising a pluralityof metal interconnect layers 108 arranged within an ILD layer 106.

A plurality of color filters 116 are arranged over the back-side of thesemiconductor substrate 102. The plurality of color filters 116 arerespectively configured to transmit specific wavelengths of incidentradiation 120. For example, a first color filter (e.g., a red colorfilter) may transmit light having wavelengths within a first range,while a second color filter may transmit light having wavelengths withina second range different than the first range. A plurality ofmicro-lenses 118 are arranged over the plurality of color filters 116.Respective micro-lenses 118 are aligned laterally with the color filters116 and overlie the pixel regions 103 a-103 c. The micro-lenses 118 areconfigured to focus the incident radiation 120 (e.g., light) towards thepixel regions 103 a-103 c.

A doped region 110 is arranged along a surface of the pixel regions 103a-103 c opposing at a location that is between the pixel regions 103a-103 c and the plurality of color filters 116. The doped region 110separates the image sensing elements 104 within the pixel regions 103a-103 c from the DTI structures 111. The doped region 110 has a greaterconcentration of dopants than the pixel region 103 a-103 c. In someembodiments, the doped region 110 may comprise a p-type region, while inother embodiments the doped region 110 may comprise an n-type region.The greater doping concentration of the doped region 110 forms a regionthat separates the image sensing element 104 from interface defectslocated along the edges of the DTI structures 111, and thereby reducesthe dark current and/or white pixel number of the CMOS image sensor 100.

FIG. 2 illustrates a cross-sectional view of some embodiments of anintegrated chip 200 comprising a photodiode 202 separated from aback-side deep trench isolation (BDTI) structure by a doped region.

The photodiode 202 comprises a first region 202 a and an underlyingsecond region 202 b arranged within the semiconductor substrate 102. Thefirst region 202 a has a first doping type and the second region 202 bhas a second doping type that is different than the first doping type.In some embodiments, the first region 202 a comprises an n-type regionand the second region 202 b comprises a p-type region.

A plurality of BDTI structures 204 a-204 b are arranged within aback-side 102 b of the semiconductor substrate 102 and extend from theback-side 102 b of the semiconductor substrate 102 to a positionlaterally separated from the photodiode 202. The plurality of BDTIstructures comprise one or more dielectric materials 112-114 arrangedwithin a trench in the semiconductor substrate 102. In variousembodiments, the plurality of BDTI structures 204 a-204 b may extend toa depth d_(BDTI) of greater than or equal to approximately 0.5 micronswithin the semiconductor substrate 102.

A doped region 110 is vertically arranged between the photodiode 202 andthe back-side 102 b of the semiconductor substrate 102. The doped region110 has an opposite doping type as the first region 202 a of thephotodiode 202 so that the doped region 110 separates the photodiode 202from the plurality of BDTI structures 204 a-204 b. For example, in someembodiments, the first region 202 a may comprise an n-type doping, whilethe doped region 110 may comprise a p-type region. In other embodiments,the first region 202 a may comprise a p-type doping, while the dopedregion 110 may comprise an n-type region.

The photodiode 202 may vertically extend to a position that abuts thedoped region 110. In some embodiments, the doped region 110 may bearranged along sidewalls of the photodiode 202, so that the doped region110 laterally separates the first region 202 a of the photodiode 202from the plurality of BDTI structures 204 a-204 b and verticallyseparates the first region 202 a from one or more dielectric materials112-114 overlying the back-side 102 b of the semiconductor substrate102. The doped region 110 laterally extends between sidewalls of theplurality of BDTI structures 204 a-204 b. For example, the doped region110 laterally extends from a sidewall of a first BDTI structure 204 a toa sidewall of a second BDTI structure 204 b.

In some embodiments, the doped region 110 may have a dopingconcentration that is greater than or equal to approximately 5e15dopants/cm³. In some additional embodiments, the doped region 110 mayhave a doping concentration that is greater than or equal toapproximately 1e17 dopants/cm³. The doped region 110 has a depth d_(P)that is less than the depth d_(BDTI) of the plurality of BDTI structures204 a-204 b, such that the plurality of BDTI structures 204 a-204 bvertically extend through the doped region 110. For example, in variousembodiments, the doped region 110 may extend to a depth d_(P) of greaterthan or equal to approximately 0.1 microns within the semiconductorsubstrate 102.

FIG. 3 illustrate cross-sectional views of some additional embodimentsof a back-side illumination CMOS (BSI-CMOS) image sensor 300 comprisinga photodiode separated from a back-side deep trench isolation (BDTI)structure by a p-type doped region.

The BSI-CMOS image sensor 300 comprises a pixel region 301 arrangedwithin a semiconductor substrate 102. In some embodiments, the pixelregion 301 may be isolated from adjacent pixel regions by one or moreisolation structures 306 (e.g., shallow trench isolation regions)arranged within the semiconductor substrate 102 on opposing sides of thepixel region 301. The one or more isolation structures 306 may comprisean insulating material arranged within a trench in a front-side 102 f ofthe semiconductor substrate 102.

The pixel region 301 comprises a photodiode 302 having a first region302 a with a first doping type (e.g., n-type doping) and a second region302 b with a second doping type (e.g., p-type doping) that is differentthan the first doping type. The first region 302 a vertically extendsfrom the second region 302 b to a p-type region 303. In someembodiments, the p-type region 303 may have a doping concentrationgreater than or equal to approximately 5e15 atoms/cm³. In someembodiments, the p-type region 303 may be arranged along a back-side 102b of the semiconductor substrate 102.

A transfer transistor 309 is arranged over the front-side 102 f of thesemiconductor substrate 102. The transfer transistor 309 comprises agate dielectric layer 308 is disposed over the front-side of thesemiconductor substrate 102 and a gate electrode 310 is arranged ontothe gate dielectric layer 308. In some embodiments, sidewall spacers 312are arranged on opposing sides of the gate electrode 310. The transfertransistor 309 is laterally arranged between the photodiode 302 and afloating diffusion well 304.

An ILD layer 106 is arranged along the front-side 102 f of thesemiconductor substrate 102. The ILD layer 106 comprises one or more ILDmaterials. In various embodiments, the ILD layer 106 may comprise one ormore of a low-k dielectric layer (i.e., a dielectric with a dielectricconstant less than about 3.9), an ultra low-k dielectric layer, or anoxide (e.g., silicon oxide). Conductive contacts 314 are arranged withinthe ILD layer 106. The conductive contacts 314 extend from the gateelectrode 310 and the floating diffusion well 304 to one or more metalwire layers (not shown). In various embodiments, the conductive contacts314 may comprise a conductive metal such as copper or tungsten, forexample.

Back-side deep trench isolation (BDTI) structures 315 are arrangedwithin the back-side 102 b of the semiconductor substrate 102 alongedges of the pixel region 301. The plurality of BDTI structures 315 maycomprise a passivation layer 316 arranged onto sidewalls of a trenchextending into the back-side 102 b of the semiconductor substrate 102. Ahigh-k dielectric layer 318 vertically and laterally separates thepassivation layer 316 from a dielectric fill layer 114 that fills in aremainder of the trench. In some embodiments, the passivation layer 316and the high-k dielectric layer 318 may extend over the back-side 102 bof the semiconductor substrate 102 between a first trench and the secondtrench. In some embodiments, the passivation layer 316 may comprise ananti-reflective coating (ARC), such as a bottom resist anti-reflectivecoating (BARC), for example. In other embodiments, the passivation layer316 may comprise an organic polymer or a metallic oxide. In someembodiments, the high-k dielectric layer 318 may comprise hafnium oxide(HfO), hafnium silicon oxide (HfSiO), hafnium aluminum oxide (HfAlO), orhafnium tantalum oxide (HfTaO), for example.

A layer of dielectric material 320 vertically separates a plurality ofcolor filters 116 from the back-side 102 b of the semiconductorsubstrate 102. In some embodiments, the plurality of color filters 116may be arranged within a grid structure 322 disposed onto the layer ofdielectric material 320. In some embodiments, the grid structure 322 maycomprise a stacked grid having a metal framework surrounded by adielectric material. In some embodiments, layer of dielectric material320 and the stacked grid may have a same dielectric material (e.g.,silicon-dioxide (SiO₂)).

A plurality of micro-lenses 118 are arranged over the plurality of colorfilters 116. In some embodiments, the plurality of micro-lenses 118 havea substantially flat bottom surface abutting the plurality of colorfilters 116 and a curved upper surface. The curved upper surface isconfigured to focus incident radiation towards the underlying pixelregion 301.

During operation of the BSI-CMOS image sensor 300 incident radiation isfocused by the micro-lens 118 to the underlying pixel region 301. Whenincident radiation of sufficient energy strikes the photodiode 302, itgenerates an electron-hole pair that produces a photocurrent. Thetransfer transistor 309 controls charge transfer from the photodiode 302to the floating diffusion well 304. If the charge level is sufficientlyhigh within the floating diffusion well 304, a source followertransistor 324 is activated and charges are selectively output accordingto operation of a row select transistor 326 used for addressing. A resettransistor 328 is configured to reset the photodiode 302 betweenexposure periods.

FIGS. 4-11 illustrate some embodiments of cross-sectional views 400-1100showing a method of forming a CMOS-BSI image sensor having doped regionseparating a photodiode from a back-side deep trench isolation (BDTI)structure.

As shown in cross-sectional view 400 of FIG. 4, a dopant species 404 isimplanted into a semiconductor substrate 402 to form a doped region 406.In various embodiments, the semiconductor substrate 402 may comprise anytype of semiconductor body (e.g., silicon/CMOS bulk, SiGe, SOI, etc.)such as a semiconductor wafer or one or more die on a wafer, as well asany other type of semiconductor and/or epitaxial layers formed thereonand/or otherwise associated therewith. In some embodiments, the dopantspecies 404 may comprise a p-type dopant (e.g., boron) that is implantedinto a front-side 402 f of the semiconductor substrate 402. In otherembodiments, the dopant species 404 may comprise an n-type dopant (e.g.,phosphorous). In some embodiments, the dopant species 404 may beimplanted into the back-side 402 b of the semiconductor substrate 402.In some embodiments, the dopant species 404 may be implanted as ablanket implantation (i.e., an unmasked implantation). In otherembodiments, the dopant species 404 may be implanted as a selectiveimplantation (i.e., a masked implantation).

As shown in cross-sectional view 500 of FIG. 5, a transfer transistor309 is formed over a front-side 402 f of the semiconductor substrate402. The transfer transistor 309 may be formed by depositing a gatedielectric film and a gate electrode film over the semiconductorsubstrate 402. The gate dielectric film and the gate electrode film aresubsequently patterned to form a gate dielectric layer 308 and a gateelectrode 310. Sidewall spacers 312 may be formed on the outer sidewallsof the gate electrode 310. In some embodiments, the sidewall spacers 312may be formed by depositing nitride onto the front-side 402 f of thesemiconductor substrate 402 and selectively etching the nitride to formthe sidewall spacers 312.

Implantation processes are performed within the front-side 402 f of thesemiconductor substrate 402 to form a photodiode 302 along a first sideof the transfer transistor 309 and a floating diffusion well 304 alongan opposite, second side of the transfer transistor 309. The photodiode302 may be formed by selectively implanting the semiconductor substrate102 with a first implantation process to form a first region 302 ahaving a first doping type (e.g., n-type), and a second subsequentimplantation process to form an abutting second region 302 b having asecond doping type (e.g., p-type) different than the first doping type.In some embodiments, the first region 302 a may vertically abut thedoped region 406. In some embodiments, the semiconductor substrate 402may be selectively implanted according to a patterned masking layer (notshown) comprising photoresist.

In some embodiments, one or more isolation structures 306 (e.g., shallowtrench isolation regions) may be formed within the front-side 402 f ofthe semiconductor substrate 402 on opposing sides of a pixel region 301.The one or more isolation structures 306 may be formed by selectivelyetching the front-side 402 f of the semiconductor substrate 402 to formshallow-trenches and subsequently forming an oxide within theshallow-trenches. In some embodiments, the one or more isolationstructures 306 may be formed prior to formation of the transfertransistor 309, the photodiode 302, and/or the floating diffusion well304.

As shown in cross-sectional view 600 of FIG. 6, a BEOL metallizationstack comprising a plurality of metal interconnect layers 108 arrangedwithin an ILD layer 106 is formed over the front-side 402 f of thesemiconductor substrate 402. In some embodiments, the BEOL metallizationstack may be formed by forming the ILD layer 106, which comprises one ormore layers of ILD material, over the front-side 402 f of thesemiconductor substrate 402. The ILD layer 106 is subsequently etched toform via holes and/or metal trenches. The via holes and/or metaltrenches are then filled with a conductive material to form theplurality of metal interconnect layers 108. In some embodiments, the ILDlayer 106 may be deposited by a physical vapor deposition technique(e.g., PVD, CVD, etc.). The plurality of metal interconnect layers 108may be formed using a deposition process and/or a plating process (e.g.,electroplating, electro-less plating, etc.). In various embodiments, theplurality of metal interconnect layers 108 may comprise tungsten,copper, or aluminum copper, for example.

As shown in cross-sectional view 700 of FIG. 7, the ILD layer 106 isbonded to a handle substrate 702. In some embodiments, the bondingprocess may use an intermediate bonding oxide layer (not shown) arrangedbetween the ILD layer 106 and the handle substrate 702. In someembodiments, the bonding process may comprise a fusion bonding process.In some embodiments, the handle substrate 702 may comprise a siliconwafer.

As shown in cross-sectional view 800 of FIG. 8, a thickness of thesemiconductor substrate 102 is reduced. Thinning the semiconductorsubstrate 102 reduces a thickness of the substrate from a firstthickness t₁ to a second thickness t₂ to allow for radiation to passthrough the back-side 102 b of the semiconductor substrate 102 to thephotodiode 302. In some embodiments, the semiconductor substrate 102 maybe thinned by etching the back-side 402 b of the semiconductorsubstrate. In other embodiments, the semiconductor substrate 102 may bethinned by mechanical grinding the back-side 402 b of the semiconductorsubstrate.

As shown in cross-sectional view 900 of FIG. 9, the semiconductorsubstrate 102 is selectively etched to form deep trenches 902 a-902 bwithin the back-side 102 b of the semiconductor substrate 102. In someembodiments, the semiconductor substrate 102 may be etched by forming amasking layer 904 onto the back-side 102 b of the semiconductorsubstrate 102. The semiconductor substrate 102 is then exposed to anetchant 906 in regions not covered by the masking layer 904. The etchant906 etches the semiconductor substrate 102 to form deep trenches 902a-902 b extending to the semiconductor substrate 102. The deep trenches902 a-902 b extend through the doped region 110 to a position within thesemiconductor substrate 102 that is laterally separated from thephotodiode 302 by the doped region 110.

In various embodiments, the masking layer 904 may comprise photoresistor a nitride (e.g., SiN) patterned using a photolithography process. Invarious embodiments, the etchant 906 may comprise a dry etchant have anetching chemistry comprising a fluorine species (e.g., CF₄, CHF₃, C₄F₈,etc.) or a wet etchant (e.g., hydroflouric acid (HF) orTetramethylammonium hydroxide (TMAH)).

As shown in cross-sectional view 1000 of FIG. 10, the deep trenches 902a-902 b are filled with dielectric material. In some embodiments, apassivation layer 316 is formed within the deep trenches 902 a-902 b anda high-k dielectric layer 318 is formed within the deep trenches 902a-902 b onto the passivation layer 316. The passivation layer 316 andthe high-k dielectric layer 318 line sidewalls and bottom surfaces ofthe deep trenches 902 a-902 b. In some embodiments, the passivationlayer 316 and the high-k dielectric layer 318 may extend over theback-side 102 b of the semiconductor substrate 102 between a first deeptrench 902 a and a second deep trench 902 b. A dielectric fill layer 114is formed to fill a remainder of the deep trenches 902 a-902 b. In someembodiments, a planarization process is performed after forming thedielectric fill layer 114 to form a planar surface that extends along anupper surface of the high-k dielectric layer 318 and the dielectric filllayer 114. In some embodiments, the passivation layer 316, the high-kdielectric layer 318, and the dielectric fill layer 114 may be depositedusing a physical vapor deposition technique.

As shown in cross-sectional view 1100 of FIG. 11, a plurality of colorfilters 116 are formed over the back-side 102 b of the semiconductorsubstrate 102. In some embodiments, the plurality of color filters 116may be formed by forming a color filter layer and patterning the colorfilter layer. The color filter layer is formed of a material that allowsfor the transmission of radiation (e.g., light) having a specific rangeof wavelength, while blocking light of wavelengths outside of thespecified range. Further, in some embodiments, the color filter layer isplanarized subsequent to formation.

A plurality of micro-lenses 118 are formed over the plurality of colorfilters 116. In some embodiments, the plurality of micro-lenses 118 maybe formed by depositing a micro-lens material above the plurality ofcolor filters 116 (e.g., by a spin-on method or a deposition process). Amicro-lens template (not shown) having a curved upper surface ispatterned above the micro-lens material. In some embodiments, themicro-lens template may comprise a photoresist material exposed using adistributing exposing light dose (e.g., for a negative photoresist morelight is exposed at a bottom of the curvature and less light is exposedat a top of the curvature), developed and baked to form a roundingshape. The plurality of micro-lenses 118 are then formed by selectivelyetching the micro-lens material according to the micro-lens template.

FIG. 12 illustrates a flow diagram of some additional embodiments of amethod 1200 of forming a CMOS-BSI image sensor having a light sensingelement separated from back-side deep trench isolation (BDTI) regions bya p-type region.

While disclosed method 1200 is illustrated and described herein as aseries of acts or events, it will be appreciated that the illustratedordering of such acts or events are not to be interpreted in a limitingsense. For example, some acts may occur in different orders and/orconcurrently with other acts or events apart from those illustratedand/or described herein. In addition, not all illustrated acts may berequired to implement one or more aspects or embodiments of thedescription herein. Further, one or more of the acts depicted herein maybe carried out in one or more separate acts and/or phases

At 1202, a dopant species is implanted into a semiconductor substrate toform a doped region. In some embodiments, the implantation is performedinto a front-side of the semiconductor substrate. In alternativeembodiments, the implantation may be performed into a back-side of thesemiconductor substrate. In some embodiments, the dopant species maycomprise a p-type dopant. FIG. 4 illustrates a cross-sectional viewcorresponding to some embodiments corresponding to act 1202.

At 1204, an image sensing element is formed within the front-side of thesemiconductor substrate. In some embodiments, the image sensing elementmay comprise a photodiode formed by implanting dopant species into thefront-side of the semiconductor substrate. FIG. 5 illustrates across-sectional view corresponding to some embodiments corresponding toact 1204.

At 1206, a transfer transistor is formed along the front-side of thesemiconductor substrate. FIG. 5 illustrates a cross-sectional viewcorresponding to some embodiments corresponding to act 1206.

At 1208, a floating diffusion well is formed within the front-side ofthe semiconductor substrate. FIG. 5 illustrates a cross-sectional viewcorresponding to some embodiments corresponding to act 1208.

At 1210, a BEOL metallization stack is formed over the transfertransistor on the front-side of the semiconductor substrate. FIG. 6illustrates a cross-sectional view corresponding to some embodimentscorresponding to act 1210.

At 1212, the BEOL metallization stack is bonded to a handle substrate.FIG. 7 illustrates a cross-sectional view corresponding to someembodiments corresponding to act 1212.

At 1214, the semiconductor substrate is thinned by removing materialfrom a back-side of the semiconductor substrate. FIG. 8 illustrates across-sectional view corresponding to some embodiments corresponding toact 1214.

At 1216, the back-side of the semiconductor substrate is selectivelyetched to form deep trenches extending into the semiconductor substrate.FIG. 9 illustrates a cross-sectional view corresponding to someembodiments corresponding to act 1216.

At 1218, the deep trenches are filled with one or more dielectricmaterials to form back-side deep trench isolation (BDTI) structuresseparated from the image sensing element by the doped region. FIG. 10illustrates a cross-sectional view corresponding to some embodimentscorresponding to act 1218.

At 1220, color filters and micro-lenses are formed over the back-side ofthe semiconductor substrate. FIG. 11 illustrates a cross-sectional viewcorresponding to some embodiments corresponding to act 1220.

Therefore, the present disclosure relates to a CMOS image sensorcomprising a doped region, arranged between deep trench isolationstructures and an image sensing element, which is configured to reducedark current and white pixel number, and an associated method offormation.

In some embodiments, the present disclosure relates to a CMOS imagesensor. The image sensor comprises a pixel region disposed within asemiconductor substrate and comprising an image sensing elementconfigured to convert radiation into an electrical signal. The imagesensor further comprises a plurality of back-side deep trench isolation(BDTI) structures extending from a back-side of the semiconductorsubstrate to positions within the semiconductor substrate located onopposing sides of the pixel region. The image sensor further comprises adoped region laterally arranged between the plurality of BDTI structuresand configured to separate the image sensing element from the pluralityof BDTI structures.

In some embodiments, the present disclosure relates to a CMOS imagesensor. The image sensor comprises a photodiode arranged within asemiconductor substrate, and a plurality of back-side deep trenchisolation (BDTI) structures extending from a back-side of thesemiconductor substrate to positions within the semiconductor substrateon opposing sides of the photodiode. The image sensor further comprisesa doped region arranged along the back-side of the semiconductorsubstrate and configured to separate the photodiode from the pluralityof BDTI structures. The image sensor further comprises aback-end-of-the-line (BEOL) metallization stack arranged on a front-sideof the semiconductor substrate and comprising a plurality of metalinterconnect layers arranged within an inter-level dielectric layer.

In yet other embodiments, the present disclosure relates to method offorming an image sensor. The method comprises implanting a dopantspecies into a semiconductor substrate to form a doped region, andforming an image sensing element within a front-side of thesemiconductor substrate. The method further comprises etching thesemiconductor substrate to form a plurality of deep trenches extendinginto a back-side of the semiconductor substrate, wherein the back-sideof the semiconductor substrate opposes the front-side of thesemiconductor substrate. The method further comprises filling theplurality of deep trenches with one or more dielectric materials to formback-side deep trench isolation (BDTI) structures that are separatedfrom the image sensing element by the doped region.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of forming an image sensor, comprising:implanting a dopant into a substrate to form a doped region; implantingone or more additional dopants into the substrate to form an imagesensing element between the doped region and a front-side of thesubstrate; etching the substrate to form one or more trenches extendinginto a back-side of the substrate after implanting the dopant into thesubstrate to form the doped region, wherein the back-side of thesubstrate opposes the front-side of the substrate; and filling the oneor more trenches with one or more dielectric materials to form isolationstructures.
 2. The method of claim 1, wherein the doped region is formedso as to be separated from opposing surfaces of the substrate bynon-zero distances.
 3. The method of claim 2, further comprising:thinning the substrate to expose the doped region along the back-side ofthe substrate.
 4. The method of claim 1, wherein the one or moretrenches extend completely through the doped region.
 5. The method ofclaim 1, further comprising: forming a plurality of conductiveinterconnect layers within one or more inter-level dielectric layers onthe front-side of the substrate.
 6. The method of claim 1, wherein thedopant is implanted into the front-side of the substrate to form thedoped region.
 7. The method of claim 1, wherein the doped region isseparated from the one or more dielectric materials along a firstdirection and along a second direction that is perpendicular to thefirst direction.
 8. The method of claim 1, wherein the doped regionextends laterally past opposing edges of the image sensing element andis arranged vertically between the image sensing element and theback-side of the substrate.
 9. The method of claim 1, wherein the dopedregion physically contacts a boundary of the image sensing element thatis nearest the back-side of the substrate.
 10. The method of claim 1,wherein filling the one or more trenches with the one or more dielectricmaterials comprises: forming a high-k dielectric material within the oneor more trenches and over back-side of the substrate.
 11. A method offorming an image sensor, comprising: implanting a dopant into afront-side of a substrate to form a doped region; forming an imagesensing element between the doped region and the front-side of thesubstrate; etching a back-side of the substrate to form one or moretrenches extending completely through the doped region on opposing sidesof the image sensing element, wherein the back-side of the substrateopposes the front-side of the substrate; and filling the one or moretrenches with one or more dielectric materials.
 12. The method of claim11, wherein the doped region extends laterally past opposing sides ofthe image sensing element.
 13. The method of claim 11, wherein the dopedregion physically contacts a boundary of the image sensing element thatis nearest the back-side of the substrate.
 14. The method of claim 11,wherein a bottom of the image sensing element facing the back-side ofthe substrate has a first width and a top of the image sensing elementfacing the front-side of the substrate has a second width that isgreater than the first width.
 15. The method of claim 11, wherein theimage sensing element has a first doped region that has a first maximumwidth and a second doped region that has a second maximum width that islarger than the first maximum width, the second doped region is betweenthe first doped region and the front-side of the substrate.
 16. A methodof forming an image sensor, comprising: implanting a dopant into asubstrate to form a doped region; forming an image sensing elementbetween the doped region and a front-side of the substrate; thinning thesubstrate to expose the doped region along a back-side of the substrateopposing the front-side; etching the back-side of the substrate to formone or more trenches; and forming one or more dielectric materialswithin the one or more trenches.
 17. The method of claim 16, wherein theone or more trenches protrude outward past the doped region towards thefront-side of the substrate.
 18. The method of claim 16, wherein thedoped region physically contacts a boundary of the image sensing elementfacing the back-side of the substrate.
 19. The method of claim 16,wherein the back-side of the substrate is etched to form the one or moretrenches after thinning the substrate.
 20. The method of claim 16,wherein the dopant is implanted into the front-side of the substrate toform the doped region.